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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 10-22-05, 02:17 PM   #1
Sincitycycler
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Any adjustments needed if you convert a 53/39 to a 50/36

Do you need a different chain or any special adjustments anywhere?
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Old 10-22-05, 02:37 PM   #2
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Quote:
Originally Posted by Sincitycycler
Do you need a different chain or any special adjustments anywhere?
Not likely to be essential, but a couple likely for optimization:

Might want to take out a link or two to keep chain tension correct.

Might want to lower the fder in accordance with the drop in the ring heights to have the fder aligned with the rings for optimal shifting.
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Old 10-22-05, 04:16 PM   #3
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Quote:
Originally Posted by Sincitycycler
Do you need a different chain or any special adjustments anywhere?
When I installed mine I lowered the front derailleur a bit, resized the chain which resulted in removing 1 inch of chain, and reprogrammed my flight Deck computer. Actually I removed, regreased and reinstalled the bottom bracket too. The whole process took a little under an hour and the only thing that I had to buy was the crankset.
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Old 10-22-05, 05:46 PM   #4
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Quote:
Originally Posted by Sincitycycler
Do you need a different chain or any special adjustments anywhere?
If you are using a Shimano probably not. Shimano double front derailleurs can handle the 14 teeth jump. There are a lot of forumites that complain about the 50/34 though.

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Old 10-22-05, 07:07 PM   #5
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But you still need to lower the derailleur on the seat-tube so that the outer-cage is 1-1.5mm above the big-ring. Or else it's going to take a LONG cable pull for the same action as before...
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Old 10-22-05, 07:11 PM   #6
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Pull will be excactly the same.
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Old 10-22-05, 07:23 PM   #7
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I changed the Bianchi from 52-42 to 50-42 without lowering the Campag. Record front derailleur, although I really should drop it a bit ...
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Old 10-22-05, 09:45 PM   #8
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Quote:
Originally Posted by sydney
Pull will be excactly the same.
Yes, the cable pull on the derailleur will the same to make the derailleur move the same amount. However with the derailleur further away from the chain, you have to move it more to bend the chain to the same angle.

Here's a good procedure for the front-derailleur from Park Tool Co.. The very first step is to make sure the derailleur is just a penny's thickness from the chainring teeth.



Assuming the front-derailleur is adjusted properly to be this close with the 53t chainring, going to a 50t will increase the gap to about 6mm, much, much too large for quick and easy shifts.

Last edited by DannoXYZ; 10-22-05 at 09:52 PM.
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Old 10-23-05, 08:48 AM   #9
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One precaution when setting the front derailleur height on Shimano cranks. Shimano's large chainrings have several short "release" teeth to improve shifting. Be sure you don't set the FD height based on one of these teeth or the normal height teeth may hit the cage plate.

Don't ask how I know this.
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